Rotating induction apparatus

ABSTRACT

An electrical rotating apparatus comprises an inverter system that outputs more than three phases. The apparatus further includes a stator comprising a plurality of slots and full span concentrated windings, with the windings being electrically coupled to the inverter system, and a rotor electromagnetically coupled to a magnetic field generated by the stator. A signal generator generates a drive waveform signal, that has a fundamental frequency, and the drive waveform signal drives the inverter system. The drive waveform signal has a pulsing frequency and is in fixed phase relation to the fundamental frequency. Additionally, the inverter system may be fed by a drive waveform signal that is fed through at least one signal delay device.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a division of application Ser. No. 09/255,291filed Feb. 22 1999 hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] This invention relates generally to rotating induction apparatusand more specifically to rotating induction apparatus that are tolerantof harmonics.

[0003] In a rotating induction apparatus, a current of electrical chargegenerated within a magnetic field experiences a force perpendicular tothe flow of charge and to the lines of force of the magnetic field. If aconductor is forced through a magnetic field by some sort of an externalprime mover, an electrical current is caused to flow; this is theprinciple of the operation of an electrical generator. When anelectrical current flows through a conductor in a magnetic field, aforce is applied to the conductor; this is the principle of theoperation of an electrical motor.

[0004] In an alternating current (AC) induction motor, a rotatingmagnetic field is produced by the stator or stationary portion of theapparatus. This rotating magnetic field interacts with current carriedby conductors of the rotor, causing the rotor to turn. It also producescurrents in the rotor conductors by transformer action. Thus, the rotorneeds no connections to an electrical supply, and is simply supported bybearings which allow free rotation.

[0005] The rotating magnetic field is produced by coils of wire orwindings, suitably positioned on the stator. Each winding, whenenergized with a direct current, would produce a fixed magnetic field.By energizing a winding with a sinusoidal AC, a smooth varying magneticfield of fixed orientation may be produced. By positioning severalwindings of differing orientations on a single stator and energizing thewindings with alternating currents of differing phase, a rotatingmagnetic field is produced which is the sum of the time-varying fixedorientation magnetic fields generated by each winding/phase. The statoris defined as the stationary part of the magnetic circuit and thesestator windings.

[0006] The rotating field produced by the stator windings is complex andirregular. By the principal of superposition, the rotating field may beanalyzed as being composed of numerous rotating fields of differentshape, including a fundamental or desired lowest frequency structure.The rotating field is composed of this fundamental field and higherfrequency harmonic fields.

[0007] The excitation currents may similarly be complex, and may beanalyzed as being composed of several different harmonic currents. Thefundamental excitation current is the primary source of torque.

[0008] Spatial harmonics, or air-gap harmonics, are harmonic fieldsgenerated by the non-sinusoidal nature of the field generated by eachwinding. When spatial harmonics are excited by the fundamental drivecurrents, they produce a secondary rotating field that rotates slowerthan the fundamental field. For a given excitation frequency, spatialharmonic fields rotate more slowly than the fundamental field.

[0009] Harmonic fields generated by non-sinusoidal drive wave-forms aretermed temporal harmonics. Rotating fields produced by temporal harmoniccurrents rotate more rapidly than the fundamental field. When temporalharmonics excite the fundamental spatial field, they produce a secondaryrotating field that rotates more rapidly than the fundamental field andmay rotate in the opposite direction to the fundamental field.

[0010] Therefore, both spatial and temporal harmonics in rotating fieldsmay adversely affect the efficiency of a conventional rotating inductionapparatus, lowering torque and increasing current flow.

BRIEF DESCRIPTION OF THE INVENTION

[0011] From the foregoing, it may be appreciated that a need has arisenfor a rotating induction apparatus that is tolerant of harmonics.

[0012] In accordance with an embodiment of the present invention, arotating induction apparatus comprises: an inverter system that outputsa number of phases, wherein the number is more than three; a statorcomprising a plurality of slots and full span concentrated windings,wherein the windings are electrically coupled to the inverter system; arotor electromagnetically coupled to a magnetic field generated by thestator; and a signal generator generating a drive waveform signal, thedrive waveform signal having a fundamental frequency, wherein the drivewaveform signal drives the inverter system, and further wherein apulsing frequency of the drive waveform signal is in fixed phaserelation to the fundamental frequency.

[0013] In accordance with another embodiment of the present invention, arotating induction apparatus comprises: an inverter system that outputstwo or more phases; a stator comprising a plurality of slots and fullspan concentrated windings, wherein the windings are electricallycoupled to the inverter system; a rotor electromagnetically coupled to amagnetic field generated by the stator; and a signal generatorgenerating a drive waveform signal, wherein the drive waveform signaldrives the inverter system and the drive waveform signal is fed to theinverter system through at least one signal delay device.

[0014] In accordance with still another embodiment of the presentinvention, a rotating induction apparatus comprises: an inverter systemthat outputs more than three phases; a stator comprising a plurality ofslots and full span concentrated windings, wherein the windings areelectrically coupled to the inverter system; a rotor electromagneticallycoupled to a magnetic field generated by the stator; and whereby theinverter system comprises at least one module, wherein the at least onemodule comprises an inverter.

[0015] In accordance with a further embodiment of the present invention,a rotating induction apparatus comprises: an inverter system thatoutputs at least six phases, wherein the number of phases is a multipleof three; a stator comprising a plurality of slots and full spanconcentrated windings, wherein the windings are electrically coupled tothe inverter system; a rotor electromagnetically coupled to a magneticfield generated by the stator; and whereby the windings are grouped intoa plurality of three phase groups, wherein the plurality of three phrasegroups is equivalent to the number of phases divided by three.

[0016] In accordance with still yet another embodiment of the presentinvention, a rotating induction apparatus comprises: an inverter systemthat outputs a number of phases, wherein the number of phases is morethan three, the inverter system comprising a number of half bridgeinverters equivalent to the number of phases; a stator comprising aplurality of slots and full span concentrated windings, wherein thewindings are electrically coupled to the inverter system, wherein halfof the windings are driven and the other half of the windings areconnected to a star point; a rotor electromagnetically coupled to amagnetic field generated by the stator; and whereby the driven windingsare arranged in at least one set of an odd integer number of windings,wherein the odd integer number of windings is the largest odd integerthat divides into the number of phases evenly and divides into 360evenly.

[0017] In accordance with still a further embodiment of the presentinvention, a rotating induction apparatus comprises: an amplifier thatgenerates an alternating current having twelve phases or greater; astator comprising a plurality of slots and full span concentratedwindings, wherein the windings are electrically coupled to theamplifier; and a rotor electromagnetically coupled to a magnetic fieldgenerated by the stator.

[0018] In accordance with yet a further embodiment of the presentinvention, a method of operating an electrical rotating apparatuscomprises: providing an inverter system that outputs more than threephases; electrically coupling full span concentrated windings of astator to the inverter system; electromagnetically coupling a rotor to amagnetic field generated by the stator; generating a drive waveformsignal from a signal generator; and driving the inverter system with thedrive waveform signal, wherein the drive waveform signal has afundamental frequency, and further wherein a pulsing frequency of thedrive waveform signal is in fixed phase relation to the fundamentalfrequency.

[0019] In accordance with another embodiment of the present invention, amethod of operating an electrical rotating apparatus comprises:providing an inverter system that outputs three or more phases;electrically coupling full span concentrated windings of a stator to theinverter system; electromagnetically coupling a rotor to a magneticfield generated by the stator; generating a drive waveform signal from asignal generator; feeding the drive waveform signal through at least onesignal delay device; and feeding a signal output from the at least onesignal delay device to the inverter system.

[0020] A technical advantage of the present invention is that itsubstantially reduces the problems associated with harmonic rotatingfields. Another technical advantage of the present invention is that itmay employ pulse width modulated signals (PWM). Further, utilizingcertain frequencies of the PWM may provide improved apparatusperformance.

[0021] A further technical advantage is that a single drive waveformsignal may be employed to drive all inverters, as opposed to employingmultiple, independent drive waveform signals.

[0022] Yet another technical advantage is that the present inventionfacilitates operation in the non-linear region of the saturation curve,or operation at densities greater than about 130,000 lines per squareinch (2.02 Tesla). Because the torque varies as the square of themagnetic field strength, operation at high saturation levelssubstantially increases available torque and motor performance duringstarting.

[0023] Still another technical advantage of the present invention isthat it may beneficially use non-sinusoidal drive waveforms produced byslow switching elements. The inverter may also use flexible componentsizes, and, therefore, facilitate cheaper per unit capacity powersemiconductors.

[0024] Other technical advantages of the present invention are set forthin or will be apparent from drawings and the description of theinvention which follows, or may be learned from the practice of theinvention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0025] For a more complete explanation of the present invention and thetechnical advantages thereof, reference is now made to the followingdescription and the accompanying drawings, wherein like referencenumerals represent like parts, in which:

[0026]FIG. 1 illustrates a schematic of the windings of an inductionapparatus of the present invention;

[0027]FIG. 2 illustrates a schematic of a twelve phase DC link inverterdrive system using half bridge drive for each phase;

[0028]FIG. 3 illustrates a schematic of a twelve phase DC link inverterdrive system using full bridge drive for each phase; and

[0029]FIG. 4 illustrates a schematic of a delay device based controllerfor the inverter system of the present invention.

[0030]FIG. 5 illustrates the formation of a drive waveform signal.

[0031]FIG. 6 illustrates a schematic of a motor stator with irregularlyspaced windings.

DETAILED DESCRIPTION OF THE INVENTION

[0032] Embodiments of the present invention and their technicaladvantages may be better understood by referring to FIGS. 1 though 4,like numerals referring to like and corresponding parts of the variousdrawings.

[0033] The present invention may utilize multiple, i.e., more thanthree, independently driven phases. Preferably, the apparatus usestwelve or more phases. Alternatively, the apparatus uses eighteen ormore phases. The present invention may be constructed on a standardinduction motor frame. Further, the embodiments of the present inventionthat utilize signal delay devices or modules are applicable with threeor more phases.

[0034]FIG. 1 illustrates a schematic of the windings of an inductionapparatus of the present invention. FIG. 1 depicts a stator 10 andinverter system 18. Inverter system 18, depicted in FIG. 1, uses halfbridge inverters, however, the present invention may utilize either halfor full bridge inverters. Stator 10 includes stator teeth 30 and slots32. Coils 12 pass through slots 32.

[0035] Inverter system 18 is comprised of a plurality of inverters, suchthat the number of inverters is equal to the number of phases desired.If inverter system 18 uses half bridge inverters, one winding end ofeach coil 12 is coupled to coil end lead 13 and is in turn coupled tolead 14. Lead 14 is coupled to an inverter in inverter system 18. Theother winding end of each coil 12 is coupled to a star point 16. Eachcoil thus has a driven end, which is the end that is coupled to theinverter system, and a back end, which is the end that is coupled tostar point 16.

[0036] If a full bridge system was being used, each end of coil 12 wouldbe coupled to a coil end lead 13, and none of the coils would beconnected to a star point 16.

[0037] When using a star point 16, or a neutral point, the number ofhalf bridges is halved. To accomplish this in the present invention,each winding has two ends or terminations. Rather than connecting aninverter to each end and driving the ends with 180 degree phasedifference, an inverter is connected to one winding end 13, and theother winding end is connected to star point 16. When the net current atstar point 16 is zero, the voltage at star point 16 will be constant,and the winding will be energized properly.

[0038] To achieve the state in which net current at star point 16 iszero, the driven winding ends may be selected to have electrical anglesthat either divide 360 degrees evenly, or be selected in independentsubsets which divide 360 degrees evenly. For example, with a twenty-fourslot stator spanning slots 1:13, twenty-four coil ends may be used, withcoil ends (driven ends) 1, 2, 4, 7, 9, 10, 12, 15, 17, 18, 20, and 23connected to a twelve phase inverter via leads and coil ends (back ends)3, 5, 6, 8, 11, 13, 14, 16, 19, 21, 22, and 24 connected to a starpoint.

[0039] The selected driven winding ends are fed with current with aphase difference that matches the electrical angles of the windings. Itis noted that the electrical angle between any two windings in thestator matches the electrical phase angle between the AC power supplyingthose windings. The electrical phase angle is the time offset in thedrive waveform between different phases, measured in degrees relative toa full cycle of the drive waveform. The electrical angle is the actualphysical angle of the winding, relative to a complete cycle (zero toNorth to zero to South to zero) of the magnetic field. For example, in atwo pole apparatus, the electrical angle is the actual physical angle.For a four pole stator, there are two magnetic cycles around thephysical stator, thus the electrical angle is twice the physical angle.For a six pole stator, there are three magnetic cycles, thus, theelectrical angle is thrice the physical angle. Accordingly, for a 2Npole stator, the electrical angle spanned is N multiplied by thephysical angle. Having the electrical phase angle of the suppliedalternating current match the electrical angle of the winding providesproper high phase order drive for the stator winding.

[0040] In addition to dividing 360 degrees evenly, the selected windingsets may contain an odd number of phases. If an even number of phases isselected, the pairs of phases have a 180 degree phase difference; suchpairs of phases then are single phases driven by a full bridge, whicheliminates the benefit of star point 16. For example, with a 30 slotstator having 15 windings each spanning 180 degrees or opposing slots,the electrical angle between each slot is 12 degrees. Because there are30 winding ends, each set of winding ends may be driven 24 degreesapart, which evenly divides the full 360 degrees, resulting in asymmetric drive with zero net current at star point 16.

[0041] Alternatively, for a 30 slot stator, 5 subsets of 3 windingseach, may be used, with each of the winding ends being 120 degreesapart. Each subset is symmetrically driven, so that the 5 subsetstogether also are symmetrically driven. Any arrangement of these 5subsets would be symmetrically driven, even if there is not regular, orirregular, angular spacing between the subsets.

[0042] The term

winding

may include a single stator conductor extending the length of a singleslot. To use coiled windings which encompasses two slots, such windingsconsist of wires that travel down one slot, around a stator end, upanother slot, and then again around the stator end back to the firstslot. When current is flowing in one direction through one slot, it isflowing in the opposite direction through the other slot. Consideringthe two slots independently, the two sides of the winding are drivenwith AC which is exactly 180° out of phase. Thus, any stator which makesuse of windings of at least a single turn has pairs of slots which are180 electrical degrees apart. Opposite halves of the same winding areplaced in magnetically opposite slots, i.e., slots that are 180electrical degrees apart.

[0043]FIG. 2 illustrates a schematic of a twelve phase DC link inverterdrive system using half bridge drive for each phase. An AC power supply22 supplies a rectifier 24. Rectifier 24 supplies DC power to halfbridges 20. Each half bridge 20 includes two controlled switches 38.Controlled switches 38 may, for example, be transistors. The apparatusdepicted in FIG. 2 depicts twelve half brides 20; the dashed outline ofhalf bridge 20 is omitted from all but the last inverter for purposes ofsimplifying the figure.

[0044] A twelve phase DC link inverter drive system is depicted; thusthere are twelve half bridges 20. Half bridges 20 alternately switchtheir output between the positive and negative DC supply. Thissynthesizes an alternating current output. The alternating currentoutput is fed, via leads 14, to windings 12.

[0045] The DC voltage used in the inverter system is known as the DCrail voltage. In comparison with a full bridge system, a half bridgeinverter system uses half the number of transistors, and, for the sameDC rail voltage, applies half the voltage to each winding. Thus, incomparison with a half bridge system, a full bridge inverter system usestwice the number of transistors, and, for the same DC rail voltage,applies twice the voltage to each winding.

[0046] Further, the half bridge drive may use various symmetries. Forexample, windings may be grouped in balanced three phase sets. A fullbridge system does not need this symmetry, because the full bridgesystem is intrinsically symmetric. Moreover, the full bridge systemplaces the full DC rail voltage on the windings, which results in thesame current flow delivering twice the power to the windings, incomparison with the half bridge.

[0047] The present invention may be configured with either full or halfbridge inverters depending on cost concerns. For example, if smaller,less expensive and less powerful transistors are desired, full bridgeinverters may be used. However, if it is more cost effective to use halfthe number of more powerful transistors, than half bridge inverters maybe more economical to use.

[0048]FIG. 3 illustrates a schematic of a twelve phase DC link inverterdrive system using full bridge drive for each phase. In this example,two half bridge 20 elements, each including two controlled switches 38,act together as a single full bridge element 21. Further, in thisexample, a twelve phase DC link inverter drive system is depicted, thusthere are twelve full bridges 21. The present invention includes greaterthan three phases, and would have a number of full bridges 21 equal tothe number of windings. Because a full bridge is comprised of two halfbridges, and each winding has a half bridge at each end, the number ofhalf bridges used with a full bridge system is equal to twice the numberof phases. Further, the apparatus depicted in FIG. 3 depicts twelve fullbride inverters 21; the dashed outline of full bridge 21 is omitted fromthe all but the last full bridge inverter to simplify the figure.

[0049] Full bridges 21 supply AC power to both ends of winding 12. Thus,using full bridges 21 doubles the power handling capacity of the device,and removes the need for a star point.

[0050] Referring again to FIG. 1, stator 10 of the present invention mayinclude a number of features. For example, stator 10 may includepole/phase groups which utilize a single slot. A pole/phase group is thewinding that comprise one phase in one pole. Further, stator 10 mayinclude a winding distribution factor of 1, or about 1, wherein thewindings are distributed across the width of a single slot.

[0051] Moreover, full span windings is used in stator 10. A full spanwinding is a winding which stretches across 180 electrical degrees ofthe stator, and thus maximally interacts with the rotating field. Fullspan winding provides a chording factor of 1, or about 1. Such windingsinclude a single coil in a single slot pair. Therefore, the full phasevoltage is applied to a single coil, necessitating high turn counts suchas with a parallel connected three phase apparatus. Consequently, eachphase carries a fraction of the entire supply current. Further, thephase angle for any phase depends on the electrical angle of the phasewinding associated with the phase.

[0052] Thus, in general, the present invention includes multiple phasewindings with full phase voltage, or a large fraction thereof, appliedto each coil. Full pitch windings may also be used, and in general,adjacent coils do not have to be connected together to form phase bands(pole/phase groups).

[0053] In three phase designs, the phase angle between adjacent phasesis 120°, with phase belts (phase bands) being placed 120° electricaldegrees apart in the stator winding. In the present invention, the phaseangle of the alternating current supplied by a given inverter outputphase is arbitrary, and defined by the inverter control system. Thephase angle between the alternating current supplied to any two phasesis simply made to be equal to the electrical angle between the coilsdriven by the phases. This electrical angle need not subdivide thestator evenly.

[0054] For example, a twelve phase, two pole apparatus may beconstructed in a twenty-four slot stator by winding twelve full spanwindings. A full span winding has a 1 to 13 pitch on a twenty-four slotstator. Each coil is 15° electrical degrees apart. Thus, the phase angleof the current supplied by each phase of the inverter system is 15°apart. Such a configuration is preferable if push-pull inverters areused which were connected to both sides of each phase coil.Consequently, the phase angle between phase twelve and phase one is165°. This is acceptable because electrical locations 180° to 345° arethe back sides of the driven coils.

[0055] Half bridges also may be used with star connected windings. Abalanced drive configuration may be achieved by driving the coil ends atslots 1, 2, 4, 7, 9, 10, 12, 15, 17, 18, 20, and 23 and star connectingthe other coil ends. In this configuration the phase angles betweenphase 1 driving the coil end at slot one are: 0°, 15°, 45°, 90°, 120°,135°, 165°, 210°, 240°, 255°, 285°, and 330°. Despite the uneven phaseangles, the motor will be driven smoothly.

[0056] Thus, the phase angle of the alternating current used to supplyeach phase may be matched to the electrical angle of each phase windingwithin the motor. Symmetry, in terms of the vector sum of all phaseangles, is utilized because of the star connection to the inverter drivesystem. However, phases need not be evenly spaced throughout the stator.

[0057] Moreover, the stator windings may be grouped into a plurality ofthree phase groups. These three phase groups may be driven byconventional three phase control electronics, and may be shut off as aunit in the event of a localized failure. By shutting down individualthree phase units, drive balance is maintained, and the apparatus iseasier to repair. Further, the apparatus is easy to operate because itis set up as a plurality of three-phase unit groups.

[0058] Flux per pole is the total magnetic current flowing through eachNorth or South pole. The magnetic flux is produced by the currentsflowing in the stator windings and is determined by the followingrelationship:${{Flux}/{pole}} = \frac{22,500,000 \times {coil}\quad {voltage}}{{frequency} \times {{turns}/{coil}}\quad \times K_{d} \times K_{s}}$

[0059] (where flux per pole is given in lines of force [10⁻⁸ Webers]coil voltage is in volts RMS, frequency is in Hertz, Kd is the windingdistribution factor [which in the present invention is about 1], and Ksis the winding chord factor [which in the present invention is about1]). For a two pole machine with a single coil per phase, phase voltageand coil voltage will be the same. For higher pole counts, windings ofcorresponding phase may be interconnected in either series or parallelconfiguration, as in conventional three phase machines, thus phasevoltage may be different from coil voltage.

[0060] A maximum flux per pole is selected based upon stator size, airgap size, and saturation considerations. Phase voltage is selected basedupon inverter design considerations. As the present inventionconstructively uses harmonics, saturation of the stator iron into thenon-linear region of the saturation curve may be used.

[0061] The present invention further includes an inverter system. Forexample, the inverter system may be a variable voltage, variablefrequency inverter system. The present invention may use a number ofinverters within the inverter system. The number of inverters is equalto the number of phases desired.

[0062] The present apparatus may also utilize a feedback system. Thefeedback system uses a controller frequency and a voltage which are bothadjusted in response to the desired operation of the rotating apparatusand to the actual measured operation. For example, if the measured speedwere below a programmed speed, the feedback control system may increasethe frequency of the AC drive. The capability of such a feedback systemis enhanced by the greater torque capability of the present invention.

[0063] In the apparatus of the present invention, stator windings, andconsequently electrical phase angles, are not necessarily evenlydistributed. Further, push-pull inverter legs may be used to drive bothsides of each phase. Additionally, high switching frequencies are notnecessary. Alternatively, a single square wave pulse per half cycle,which is low speed switching, also may be used. Moreover, as manyinverters are effectively operating in parallel, the apparatus of thepresent invention provides improved fault tolerance.

[0064] The inverters in the inverter system generate alternatingcurrent. Each inverter half-bridge generates a single phase of AC. Allof the inverters generate AC of the same voltage and frequency; thedifference between the phases is a time difference. A sine wave may bedescribed by its amplitude, its frequency, and its offset (e.g., whereit crosses zero or starts). The inverters are generating AC where thecycles start at different points in time. The time difference may bedescribed in terms of the total duration of a single AC cycle, in afashion similar to describing the number of PWM pulses per AC cycle. Afull AC cycle has a duration of 360 degrees, and the time differencebetween two different AC waveforms of the same frequency and amplitudeis measured in degrees.

[0065] The present invention may be applied to a standard squirrel cageinduction motor frame, e.g., an induction motor in which the secondarycircuit consists of a squirrel-cage winding arranged in slots in thecore. In this machine, the region of interaction between the stator andthe rotor may be considered the surface of a cylinder. Rotation is aboutthe axis of the cylinder, lines of magnetic flux pass radially throughthe cylinder surface, and current flowing in both the stator and therotor conductors is parallel to the axis of the cylinder. The presentinvention may also be applied to pancake motors or other axial fluxapparatus. The region of interaction, or air gap, is the surface of adisk. Rotation is about the axis of the disk, lines of magnetic fluxpass axially through the disk surface, and current flows radially inboth the stator and the rotor. Moreover, several rotors and stators maybe stacked.

[0066] In the present invention, output torque capability of theapparatus increases as the square of the flux density. Therefore, it isadvantageous to increase the design flux density. In a conventionalthree phase apparatus, increased flux density would produce harmoniclosses; however this is not the case with the present invention. In thepresent invention, harmonic rotating fields generated by non-linearsaturation effects, rotate in synchronism with the fundamental rotatingfield. This allows the present invention to operate in the non-linearregion of the saturation curve, where the saturation curve is therelation between the applied magnetic induction and the resultantmagnetic field.

[0067] In the present invention, flux densities of at least 150,000lines per square inch (2.33 Tesla) may be used. Further, the presentinvention may also be used at conventional flux densities (of about110,000 to 130,000 lines per square inch or 1.71 to 2.02 Tesla) whilebeing used in over voltage operation for short period overloads, i.e,operating at flux densities above conventional flux densities for shortperiods of time. The maximum torque capabilities may be increased by atleast about 200% through the use of high flux densities. For example,given a conventional induction apparatus frame and rotor, with peaktorque of 250% of nominal rated torque, the method of the presentinvention may be applied to the same frame and rotor, enabling a peaktorque of 500% nominal rated torque, for short periods of time limitedby motor heating.

[0068] With a twelve phase two pole apparatus of the present invention,a phase angle of fifteen degrees between adjacent phases is used.However, if a phase angle of forty-five degrees is employed, then theapparatus operates as a six pole apparatus. The maximum pole count,which may be used, is equal to the number of stator slots. In general,to change the pole count, the phase angle of the drive waveform signalis increased by odd integral multiples, which in turn increases the polecount of the magnetic field by the same amount of odd integralmultiples. If half turn windings are used, then even integral changes inpole count may be made, however, if full turn windings are used, then aneven pole count change places opposite winding halves at the sameelectrical angle. The use of high pole counts may be beneficial when thepresent invention is operated at high saturation levels.

[0069] Further, pole changing capability may be used to reduce statorsaturation when operating at high saturation levels. It should be notedthat any winding symmetries necessitated by the coil form or star pointneutrality used should be maintained for alternative pole counts. Inthis respect, the full bridge drive is more flexible than the halfbridge drive because the symmetry does not have to be changed.

[0070] The inverter system used in the present invention may becomprised of a number of individual inverters that are powered bymultiple drive waveform signals. Alternatively, the inverters may besupplied by one drive waveform signal, as depicted in FIG. 4. The drivewaveform signal is the command signal for the inverters.

[0071]FIG. 4 illustrates a schematic of a delay device based controllerfor the inverter system of the present invention. The delay device basedcontroller comprises inverters, a signal generator 110, and signal delaydevices 120. Signal generator 110 produces a representation of thedesired drive waveform signal. The drive waveform signal may be a PWMsquare wave, however, analog representations or digital numericrepresentations, or other signal modulation schemes may be used. Therepresentation of the desired drive waveform signal is coupled directlyto an inverter 130 and to a signal delay device 120. The output 140 ofinverter 130 is a single phase used to drive the rotating machine of thepresent invention. The output of signal delay device 120 is connected toa second inverter 132 and to a second signal delay device 122. Theoutput 142 of inverter 132 is a single phase used to drive the rotatingmachine of the present invention, offset in time by signal delay device120. The delay time of signal delay device 120 is selected to equal thedesired phase angle delay at the drive waveform frequency. Further delaydevices and inverters are added until the necessary inverter count isreached. For example, in a system with n inverters, a previously offsetsignal is sent to both signal delay device 124 and (n−1)^(th) inverter134, which outputs 144, and the output of signal delay device 124 isthen fed into the nth inverter 136, which outputs 146.

[0072] The controller described herein, which uses signal delay devices,may be used with a rotating induction apparatus having two phases ormore. To use this controller with a three phase system, two signal delaydevices are used, each providing a delay of 120°. Further, the drivewaveform signal may be analog or digital. Moreover, the signal delaydevice may be an analog or digital signal delay device.

[0073] The time delay of the signal delay devices matches the desiredphase angle. For fixed delay signal delay devices, this results in afixed frequency operation. However, signal delay devices may be clockbased; for example shift registers and circular memories, as well asbucket brigade devices and switched capacitor signal delay lines. Forthese devices, the shift clock may be supplied by the same clock usedfor waveform synthesis, such as a main system clock. Alternatively, thesignal delay devices may use a separate clock. Alternatively still, theclock signal used by the signal delay devices may be generated by thesignal generator. When the clock is tied to both the signal generatorand the signal delay devices, the drive frequency may be simply changedby altering the frequency of this clock. This clock need not be regular,and may be modulated between pulses to simplify output voltage control.Further, the clock does not need to have a fixed frequency.Additionally, speed changes made be implemented instantly by alteringthe clock used by the signal delay device.

[0074] While the number of signal delay devices depicted in FIG. 4 isone less than the number of phases, various symmetries may be exploitedto simplify the delay logic, such as an inversion. A delay of 180° issimply an inversion. Thus, delays of greater then 180° may be consideredan inversion plus a suitable delay less than 180°. For example, with aneven number of phases, the number of signal delay devices may be reducedby a factor of two because the inversions of the delayed signals from 0°to 180° produce similar results for 180° to 360°. For the fundamentaland all odd harmonics, an inversion is equal to a delay of 180°. For alleven harmonics, an inversion is equal to a delay of 360°. Thus,inversions operate most effectively where odd harmonics predominate.

[0075] Another example of a beneficial symmetry when using a full bridgeinverter, is by inverting each signal. This may be accomplished byhaving a signal fed directly into one half bridge, and an inversion ofthat signal be fed into the other half bridge. Thus, half the signaldelay devices are used to drive all of the half bridges.

[0076] Additionally, various three phase control microprocessors may beused by the present invention, which synthesize three phases of PWMoutput. These three outputs may be used to drive three (or six, if usingfull bridge) inverters in a three phase set, and the three phase signalsmay be fed through suitable delay devices to further three phase sets.

[0077] The signal delay device may be any device capable of delaying theinputted drive waveform signal. For example, the signal delay device maybe any first-in-first-out (FIFO) buffer, such as a shift register,circular memory, bucket brigade, acoustic delay line, optical delayline, mercury delay line, surface acoustic wave (SAW) delay line,inductor capacitor (LC) delay line, a liner group delay all pass filter,a wave guide, or the like.

[0078] Alternatively, one signal delay device may be used, such that thesignal delay device is able to handle multiple shifts, such as amultiple tap shift register. For example, when using 1024 bits perphase, an 18,432 bit shift register with 18 taps each 1024 bits apartmay be used. Further, because numerous delays of the same length may beused, conventional parallel memory addressed in a circular fashion mayalso be useful.

[0079] Alternatively, the signal generator may generate a drive waveformsignal that feeds a number of signal delay devices that are in parallel.This is accomplished by copying the drive waveform signal once for eachinverter. All of the copies are then sent to a bank of signal delaydevices. Each signal delay device may be set to create a delay thatgenerates a different phase. For example, for nine phases, the firstsignal delay device may create the delay of 40°, the second signal delaydevice may create a delay of 80°, and so on up until all phases arecreated. The signal for 0° may come directly from the signal generator,as no delay is needed in that signal.

[0080] Using a signal delay device is advantageous because one signalmay be used to operate any number of phases. The one signal is simplyoffset the appropriate amount of time for the number of phases in theapparatus, where time is measured as an angle relative to a full cycle.For example, if 15 phases were used, with half bridges, then the signalmay go through 14 signal delay devices that offset each signal by 24°from the previous signal.

[0081] If the number of desired phases is changed, instead of having tocreate a large set of new signals, the delay from the signal delaydevices could just be adjusted; by adding new phase drive electronicsand adjusting the number of total bits per cycle of the AC the delayangle represented by a fixed delay length is changed to match the newnumber of phases. For example, with a digital signal and eighteen phasesusing half bridges the bit stream of the drive waveform signal is 36,864bits (36×1024). Again, because half is used, 36,864/36=1024 bitrepresents a 10° phase difference. Additionally, inversion may be used;a delay line of half the length may be used to span one half of thedelay needed, with the other half being supplied by inversions.

[0082] The apparatus of the present invention also may be of modularconstruction. This is another method of allowing the apparatus to easilyadjust to a different motor having a different number of phases. Theapparatus may be made modular by placing a half bridge or full bridgedrive, whichever was being used, in a module. The number of modulesneeded for any particular apparatus is determined by the number ofphases. For example, when changing from a system of 9 phases to 15phases, 6 modules are added to the apparatus. Accordingly, by providingmodular construction, one controller and multiple modules may be used onvarious motors with different phases. Moreover, the modularity allowseasier maintenance of the apparatus.

[0083] Further, signal delay devices also may be included in themodules. Therefore, each module may include a half bridge and a signaldelay device to carry the signal to the next half bridge in theapparatus. The signal generator then may be connected to the same numberof modules as are number of phases in the apparatus. The signalgenerator is programmed with the number of modules, the total delay, andany other information that the signal generator deemed necessary tocreate the drive waveform signal. Regardless, the signal generator stillmay use just two relevant outputs: (i) the bit stream comprising thedrive waveform signal; and (ii) the delay line clock to control thelength of the delays.

[0084] If using signal delay devices in the module, the controller mayaccommodate the difference in delays from the different phases invarious apparatus by adjusting the length of the representation of theinput drive waveform signal. For example, with a digital signal, theapparatus may be programed to shift 1024 bits (2¹⁰) for every phase. Fora 9 phase apparatus, the length of the input drive waveform signal maybe 9,216 bits (9×1024). If a 15 phase apparatus was used, the length ofthe input drive waveform signal simply may be increased to 15,360 bits(15×1024). Thus, regardless of the number of phases, 1024 bits areshifted, which is equivalent to one phase for each phase shift. Further,the hardware need not be adjusted as the drive waveform signal may bealtered via software or by the signal generator that creates the inputdrive waveform signal. Alternatively, the input drive waveform signalmay be based on any other amount of bits other than 1024, however, 1024bits is preferred because it provides enough data for adequate voltageresolution and is easy for the signal delay devices to utilize. Whilethe voltage resolution depends on the length of the drive waveformsignal compared to the number of pulses per AC cycle, when the length isequal to twice the number of pulses per AC cycle, the voltage resolutionis about 0.1%. Thus, 1024 bits provides a desired voltage resolution forall practical pulses per AC cycle.

[0085] Additionally, the present invention may utilize a PWM as thedrive waveform signal. Referring now to FIG. 5, a desired drive waveformhaving a fundamental frequency 40 is approximated by a duty cyclemodulated square wave 42 (the pulsing frequency). The desired drivewaveform may be described in terms of amplitude, frequency, and phase.The duty cycle modulated square wave may be described in terms ofswitching or PWM period 44, positive amplitude 45 and negative amplitude46. The synthesized PWM output voltage waveform produces current throughmotor windings, which closely approximates that which would have beenproduced by the desired output waveform. A microcontroller system usedwith three phase motors may be used, under software control, to developthe PWM control signals for each of the three inverter phase outputs.Further, by adding additional output subroutines and using additionaloutput lines, a three phase microcontroller may be used to control allof phase outputs in the present invention.

[0086] The pulsing frequency of the PWM is specified in pulses per ACcycle. Alternatively, the pulsing frequency of the PWM may be in pulsesper radian, however, that is converted to pulses per AC cycle bymultiplying the pulses per radian by 2π. Nevertheless, the pulsingfrequency of the PWM, as used herein, is in pulses per AC cycle.

[0087] The PWM waveform is modulated to obtain an approximation of adesired sine wave. The frequency of that desired sine wave is thefundamental frequency.

[0088] There are various conditions that may affect the PWM's effect onthe apparatus. For example, there may be regular spaced windings orirregular spaced windings. Referring now to FIG. 6 the locations of thestator slots 32 need not be regularly spaced. In FIG. 6, the stator has30 slots, for a 15 phase system. The 30 slots are arranged as 15 slotpairs 32 and 60, each slot pair carrying a single phase winding. The 15slot pairs 32 and 60 are arranged as 3 sets of 5 slot pairs. Each set of5 slot pairs is symmetrically arranged to provide for balanced drive.The 3 sets of 5 slot pairs are not evenly spaced. Other conditions thatmay affect the apparatus include: (i) the PWM may be in fixed phaserelation to the fundamental frequency or not be in fixed phase relationto the fundamental frequency; (ii) the PWM may be regular or irregular;or (iii) the PWM may have a frequency above or below the phase count. Analternating current having harmonics in fixed phase relation to thefundamental frequency means that all of the harmonics in all of thephases of the alternating current have the same time relation to thefundamental frequency driving each phase. This means that the shape ofthe drive waveform is the same going into each phase.

[0089] While in a three phase system, PWM torques are always adverse, inthe present invention these torques may be either beneficially used ornegated. For example, when the PWM waveform is in fixed phase relationto the fundamental and is an even multiple of the phase count, such astwice the phase count, with the windings being regularly spaced, theharmonic currents do not enter the apparatus. Thus, having the PWMwaveform in fixed phase relation to the fundamental and twice the phasecount is advantageous, for one reason, because no additional noise iscreated by the harmonics.

[0090] When the pulsing frequency is less than the number of phases inthe apparatus, then the harmonics created from the pulsing causeadditional currents to flow into the apparatus. When current flows intothe apparatus under this condition in the present invention, theharmonic rotating fields created by pulsing currents are synchronizedwith the fundamental frequency. This results in additional torque beingcreated. However, this additional torque is beneficial in that it isapplied in the direction and speed that the motor is turning. Therefore,when the pulsing frequency is in fixed phased relation with thefundamental frequency, and is less than the number of phases in theapparatus, the efficiency of the apparatus is improved and the currentnoise is significantly reduced.

[0091] Further, when the PWM waveform is not in fixed phase relation tothe fundamental, this produces a non-beneficial rotating field. However,the PWM may be at a high enough frequency that the rotating fieldproduced may be small and may have no noticeable effect on theapparatus. Nevertheless, the effects are noticeable when the PWM is at aslow frequency.

[0092] Moreover, the PWM may be a square wave, such that the invertersare driven by a single positive and a single negative pulse for eachdesired fundamental cycle. The square wave may be, for example, a fullsquare wave or a duty cycle modulated square wave. Further, the squarewave may be a single square wave pulse per half cycle, which is lowspeed.

[0093] As stated above, harmonics that are in fixed phase relation tothe fundamental may produce beneficial harmonic rotating fields. Asquare wave comprises a fundamental sine wave, of the same frequency asthe square wave, and various quantities of odd harmonics-with theproportions of the odd harmonics varying depending on the duty cycle ofthe square wave.

[0094] A square wave, however, in comparison to a sine wave, is easy toimplement and may be used inexpensively. Because the apparatus of thepresent invention utilizes harmonics, simple, efficient square waveinverters may be used with the present invention.

[0095] In conventional three phase apparatus, to avoid losses due toharmonics, higher switching speeds are used. Conversely, because thetransistors that generate square waves may be switched slowly, theyproduce less electrical noise than with high speed switching. Therefore,the apparatus will be audibly quiet in operation.

[0096] The apparatus of the present invention may also be powered by asource of alternating current other than an inverter. For example, thealternating current may be a pure alternating current, a high phaseorder cycloconverter, or a high phase order generator may also be used.Alternatively, an amplifier may be used to generate the alternatingcurrent.

[0097] Using alternating current would eliminate the need for invertersor an inverter system. The stator may be powered directly by thealternating current having greater than three phases. This system maythen be used with any of the above modifications and maintains theadvantages detailed above.

[0098] The alternating current used may have more than three phases.Preferably, the alternating current has twelve or more phases.Alternatively, the alternating current has eighteen or more phases.

[0099] Force in a rotating induction apparatus is produced by theinteraction of rotor currents and the stator magnetic field. For anyparticular motor design, saturation effects limit the magnetic flux perunit area of interaction between rotor and stator. Because the currentsin the rotor are induced by this magnetic flux, saturation effectsfurther limit the current per unit area. Force per unit area isproportional to the product of magnetic flux per unit area andtransverse current per unit area; design changes which increase theallowable magnetic saturation will therefore increase the force per unitarea.

[0100] Force per unit area may therefore be used to compare variousrotating induction apparatus designs. However force per unit area is avalue which is rarely recorded for such apparatus. Torque values,however, are universally recorded. Torque is the moment of force, thatis, torque is the product of force time distance from the axis ofrotation. Force per unit area, when multiplied by the total area, andwhen again multiplied by the distance of that area from the axis ofrotation, will provide the total torque. It should be noted that if theradial distance of the air gap is not constant, as in axial fluxmachines, this calculation will need to be performed as an integral overthe total area.

[0101] Thus, torque divided by the moment of interaction area may beused as an equivalent to force per unit area. For a radial flux rotatinginduction apparatus, such as squirrel cage motor or generator, themoment of interaction area is the area of the air gap cylindermultiplied by the radius of said cylinder. Dropping a constant of 2π,this is the same as the equation for the volume of the rotor. Thus for arotating induction apparatus, torque divided by rotor volume may be usedas an equivalent to force per unit area.

[0102] The present invention uses torques created by harmonics to moreefficiently operate the apparatus. Based on operating at a flux densityof 150,000 lines per square inch (2.33 Tesla) the present inventionprovides an increase of at least 33% in peak torque versus rotor volumefor otherwise similar rotating induction apparatus operating at thecurrent conventional maximum of 130,000 lines per square inch (2.02Tesla). When operating at 200,000 lines per square inch (3.11 Tesla),the present invention provides an increase of at least 137% in peaktorque versus rotor volume for otherwise similar rotating inductionapparatus operating at the current conventional maximum of 130,000 linesper square inch (2.02 Tesla).

[0103] The present invention is also applicable as an electricalgenerator. To use the present invention as an electrical generator,mechanical power is supplied to the rotor and the source of power to theinverters is modified to consume the power the apparatus is nowgenerating. Any technology used for inverter controlled three phasemachines, which provide regenerative breaking capabilities, may also beapplied to the present invention.

[0104] As mentioned above, when a half bridge drive and a star pointconnection is used, windings should evenly divide 360 electricaldegrees, or evenly divide 360 electrical degrees in subsets. Thismaintains a net zero current flow in the star point; as much currentflows out of the star point and into the windings as into the star pointand out of the windings. The star point may be connected to the neutralof the DC supply, in which case any drive imbalance appears as currentin this neutral connection. Alternatively, the neutral point may beunconnected, in which imbalance in the drive is evidenced by a varyingneutral voltage. Drive imbalance may reduce the effective voltageapplied to the windings, or may result in uneven winding heating.

[0105] Similar beneficial symmetries may be used for winding positionrelative to drive waveform harmonic content. These symmetries may beexploited in a number of different ways. As mentioned above, when thedrive PWM pulses are in fixed phase relation to the fundamental, and thenumber of pulses per fundamental cycle are twice the number of phases,then the PWM pulses are a harmonic of the fundamental cycle, yet do notenter the apparatus. This occurs because, relative to the pulsingwaveform, the phase angle difference between adjacent phases is equal to360 degrees, or a multiple of 360 degrees. This means that the samevoltage is applied to all phases at the same time. As there is novoltage difference for this harmonic, this harmonic will not flow in thewindings.

[0106] If it is desired to permit a particular harmonic to flow in theapparatus, then the driven winding ends selected, described in terms ofelectrical phase angle relative to that harmonic, have a vector sum ofzero. As it is desired to use low order harmonics to supply additionaltorque, driven winding ends should be selected to pass low orderharmonics. This occurs when the winding ends selected divide 360 degreesevenly in the largest sets possible, preferably in a single set ratherthan subsets.

[0107] For example, the following are preferred winding end selectionsfor half bridge drive of star connected high phase order windings forvarious slot counts. The following are listed in terms of anglesrelative to a reference zero degree phase, which is always a drivenphase. Slot counts are relative to each two poles. Thus, for a four polemachine, the slot count is doubled. Similarly, for a 2N pole countmachine, slot count is multiplied by N. Phase count is equal to one halfthe listed slot count. Thus, it is preferable to arrange the drivenwindings of the stator in the largest sets of numerically odd subsetsthat evenly divide 360 degrees evenly, with the sets being grouped intothree phase sets, in the following electrical angles:

[0108] a) For a 9 phase winding [set of nine as three sets of threephases each]: 0°, 120°, 240°, 40°, 160°, 280°, 80°, 200°, and 320°;

[0109] b) For a 10 phase winding [two sets of five]: 0°, 18°, 72°, 90°,144°, 152°, 216°, 234°, 288°, and 306°;

[0110] c) For a 12 phase winding [four sets of three maximallydistributed]: 0°, 120°, 240°, 15°, 135°, 255°, 45°, 165°, 285°, 90°,210°, and 330°;

[0111] d) For a 15 phase winding [one set of fifteen as five sets ofthree phases each]: 0°, 120°, 240°, 24°, 144°, 264°, 48°, 168°, 288°,72°, 192°, 312°, 96°, 216°, and 336°;

[0112] e) For a 18 phase winding [two sets of nine as three sets ofthree phases each]: 0°, 120°, 240°, 10°, 130°, 250°, 40°, 160°, 280°,50°, 170°, 290°, 80°, 200°, 320°, 90°, 210°, and 330°;

[0113] f) For a 20 phase winding [four sets of five]: 0°, 9°, 27°, 54°,72°, 81°, 99°, 126°, 144°, 153°, 171°, 198°, 216°, 225°, 243°, 270°,288°, 297°, 315°, and 342°;

[0114] g) For a 24 phase winding [eight sets of three maximallydistributed]: 0°, 120°, 240°, 15°, 135°, 255°, 30°, 150°, 270°, 45°,165°, 285°, 52.5°, 172.5°, 292.5°, 67.5°, 187.5°, 307.5°, 82.5°, 202.5°,320.5°, 97.5°, 217.5°, and 337.5°;

[0115] h) For a 30 phase winding [two sets of fifteen as five sets ofthree phases each]: 0°, 120°, 240°, 6°, 126°, 246°, 24°, 144°, 264°,30°, 150°, 270°, 48°, 168°, 288°, 54°, 174°, 294°, 72°, 192°, 312°, 78°,198°, 318°, 96°, 216°, 336°, 102°, 222°, and 342°; and

[0116] i) For a 36 phase winding [four sets of nine as three sets ofthree phases each]: 0°, 120°, 240°, 5°, 125°, 245°, 15°, 135°, 255°,30°, 150°, 270°, 40°, 160°, 280°, 45°, 165°, 285°, 55°, 175°, 295°, 70°,190°, 310°, 80°, 200°, 320°, 85°, 205°, 325°, 95°, 215°, 335°, 110°,230°, and 350°.

[0117] Additionally, similar sets may be used with windings of othernumbers of phases.

EXAMPLE

[0118] The invention may be further clarified by consideration of thefollowing example, which is intended to be purely exemplary of thestructure of the invention.

[0119] In an example, an 18 phase half bridge drive embodying thepresent invention had electro-windings with the connections as detailedin Table 1. A motor was custom wound on a standard frame from which theproduction winding was removed. The frame used was from a two pole,totally enclosed, fan cooled, size 215T apparatus. This apparatus wasoriginally rated at 10 horsepower (8 kW) at 3525 RPM. Internally, theapparatus had a thirty-six slot stator and a squirrel cage rotor withcast aluminum conductors. The apparatus was rewound with a eighteenphase, two pole stator winding with all coil ends brought out toexternal termination. Coil span was 1 to 19, giving a full span winding,and 50 turns per coil was used.

[0120] The inverters used International Rectifier Corporation IR2233interface chips and were printed circuit and hardwired wrapped units,using Siemens BSM 75 GB IGBT transistor modules as the power devices. Noprovision was made for the DC supply, and a standard laboratory supplywas used as the primary DC power source for testing. Six, three phaseinverters were used to supply eighteen independent phases to the motor.

[0121] Logic control for the inverter systems was provided by a generalpurpose IBM compatible computer. Eighteen bits of parallel output wereused to supply the on/off coding to the IR2233 controller chips.Software running on the computer provided PWM of appropriate phasing tooperate the motor. Phase angle was adjustable in order to demonstratepole changing. Additionally, output wave-form was adjustable. TABLE 1Physical Drive Relation Phase Angle (from Termination Slot Anglereference) 1 1  0°  0° 2 19 180° star 3 2  10°  10° 4 20 190° star 5 3 20°  20° 6 21 200° star 7 4  30°  30° 8 22 210° star 9 5  40°  40 10 23220° star 11 6 500°  50° 12 24 230° star 13 7  60° star 14 25 240° 240°15 8  70° star 16 26 250° 250° 17 9  80° star 18 22 260° 260° 19 10  90°star 20 28 270° 270° 21 11 100° star 22 29 280° 280° 23 12 110° star 2430 290° 290° 25 13 120° 120° 26 31 300° star 27 14 130° 130° 28 32 310°star 29 15 140° 140° 30 33 320° star 31 16 150° 150° 32 34 330° star 3317 160° 160° 34 35 340° star 35 18 170° 170° 36 36 350° star

[0122] The present invention is applicable to all geometries of the ACinduction apparatus. The present invention is further applicable to bothsquirrel cage and wound rotor apparatus, which includes buriedconductors and three phase and high phase order wound rotors.

[0123] Additionally, the present invention is also applicable to alldifferent inverter topologies that have been used in the operation ofthree phase apparatus. These include voltage mode pulse width modulationinverters, which provide an alternating current regulated to a specifiedRMS voltage, current mode pulse width modulation inverters, whichprovide an alternating current regulated to a specified RMS current.Further, linear inverters which provide true continuous output, bothcurrent mode and voltage mode, may be used. DC link inverters, resonantlink inverters, and cycloconverters, all of which are different modes ofsupplying power to the inverter phase outputs, also may be used. Powerfactor correction hardware may be used on the power inputs of theinverter drive system, and regeneration capability also may be afunctional part of the inverter drive system. Square wave inverters withhigh harmonic content in the output wave form also may be used.Moreover, push-pull inverters also may be used, doubling the effectivevoltage capability of the inverter drive system, at the expense of usingmore active devices.

[0124] Further, the present invention is applicable to geometries inwhich the region of interaction between stator and rotor has circularsymmetry about the axis of rotation, magnetic flux is generally normalto the region of interaction, and current flow is generallyperpendicular both to flux and the direction of motion. Alternativegeometries which may be utilized in the method of the present inventionare axial flux, or pancake, motors, radial flux geometries in which therotor is external to the stator, or geometries which use a combinationof axial and radial flux, or multiple axial flux paths. Of particularinterest is the latter geometry, wherein a dual-sided pancake stator issurrounded on both faces by pancake rotor.

[0125] While this invention has been described with reference toillustrative embodiments, it is to be understood that this descriptionis not intended to be construed in a limiting sense. Modifications toand combinations of the illustrative embodiments will be apparent topersons skilled in the art upon reference to this description. It is tobe further understood, therefore, that changes in the details of theembodiments of the present invention and additional embodiments of thepresent invention will be apparent to persons of ordinary skill in theart having reference to this description. It is contemplated that suchchanges and additional embodiments are within the spirit and true scopeof the invention as claimed below.

1. An electrical rotating apparatus comprising: an inverter system thatoutputs more than three phases; a stator comprising a plurality of slotsand full span concentrated windings, wherein said windings areelectrically coupled to said inverter system; a rotorelectromagnetically coupled to a magnetic field generated by saidstator; and whereby said inverter system comprises at least one module,wherein said at least one module comprises an inverter.
 2. Theelectrical rotating apparatus of claim 1, wherein said inverter systemoutputs twelve or more phases.
 3. The electrical rotating apparatus ofclaim 1, wherein said inverter system outputs eighteen or more phases.4. The electrical rotating apparatus of claim 1, wherein said invertersystem comprises at least two modules.
 5. The electrical rotatingapparatus of claim 4, wherein the number of modules is less than orequal to the number of phases output from said inverter system.
 6. Theelectrical rotating apparatus of claim 4, wherein the number of modulesequals the number of phases output from said inverter system.
 7. Theelectrical rotating apparatus of claim 1, wherein said at least onemodule comprises at least one controlled switch.
 8. The electricalrotating apparatus of claim 7, wherein said at least one controlledswitch is a transistor.
 9. The electrical rotating apparatus of claim 1,wherein said at least one module further comprises a signal delaydevice.
 10. The electrical rotating apparatus of claim 1, wherein saidat least one module comprises a controlled switch and a signal delaydevice.
 11. The electrical rotating apparatus of claim 1, furthercomprising: a signal generator generating a drive waveform signal. 12.The electrical rotating apparatus of claim 11, wherein said drivewaveform signal drives said inverter system and said drive waveformsignal has a fundamental waveform component.
 13. The electrical rotatingapparatus of claim 12, further wherein said drive waveform signal has apulsing waveform component, wherein said pulsing component is in fixedphase relation to said fundamental waveform component.
 14. Theelectrical rotating apparatus of claim 13, wherein the number of pulsesof said pulsing waveform component per cycle of said fundamentalwaveform component is less than the number of phases.
 15. The electricalrotating apparatus of claim 13, wherein the number of pulses of saidpulsing waveform component per cycle of said fundamental waveformcomponent is equal to an even multiple of the number of phases.
 16. Theelectrical rotating apparatus of said claim 1, wherein said apparatus isoperated in a non-linear region of a saturation curve of said stator.17. The electrical rotating apparatus of claim 1, further wherein apulsing frequency of said drive waveform signal is not in fixed phaserelation to said fundamental frequency.
 18. The electrical rotatingapparatus of said claim 1, wherein said apparatus is operated atdensities greater than 150,000 lines per square inch (2.33 Tesla).